In recent years, digital content such as music, movies and games can be easily obtained through distribution via the Internet, digital broadcasting or package media. When copying or moving these digital content and their rights between a plurality of terminals, it is usually not allowed to move them limitlessly, although copying or moving the content only within a certain range is permitted.
It is generally considered that copying and moving is permitted only among a plurality of terminals owned by a single user. In order to realize such a restriction that allows copying and moving only within a certain range, it is necessary that a group of terminals be formed within which copying and moving among each other is allowed.
Until now, it has been assumed that this kind of group determination is performed by a server (a group determination terminal). The following is a brief explanation of a group determination processing performed by a server.
The conventional group determination system includes a server, which determines a group, and a plurality of terminals that are controlled by and connected with the server so that communication is possible via network. The server holds group lists of terminals that belong to each group. A group list means, for example, information that associates a group identifier with terminal identifiers.
In a group determination system structured as described above, group determination is carried out as follows. First, in order for a controlled terminal to acquire a group list of devices that the terminal itself belongs to, the terminal sends a terminal list requesting data to a server. In this terminal list requesting data, information such as the terminal's own terminal identifier and group identifier are included. According to the information included in the terminal list requesting data, the server sends to the requesting terminal a group list that corresponds to the information. By obtaining group information of the group that a controlling terminal belongs to through these procedures, a controlled terminal is able to realize group determination.
For example, in a conventional member identification method for identifying groups, a host terminal broadcasts packets of data that include the name of all the members as well as a network address unique to the host terminal. Each member terminal, then, analyzes the received packets and identifies the information retrieved from a packet that has its name in it, and sends a packet that includes the names of each member and the network addresses unique to each member terminal as data to the host terminal. The host terminal, then, analyzes the received packets, and if the host terminal finds the name of a member that belongs to the same group, the host terminal obtains the information included in the packet, corresponds the member name and a terminal address, and saves the corresponding data (for an example, see the Japanese Laid-Open Patent Application No. H10-23028 as reference).
First, to explain problems that this conventional group determination method has, it is considered that in this method, a parent-child relationship occurs between a server terminal (group determination terminal) and terminals that are controlled by the server, and thus the server terminal and the controlled terminals must have different functions.
Next, the situation when a conventional determination method is applied to home electric appliances generally used by end users is considered. In order to apply a conventional determination method, a user must understand the parent-child relationships of home appliances he/she owns, and must consider how to set parent-child relationships between the appliances when he/she purchases any home electric appliance. This is because a server terminal is indispensable in the group determination and it is assumed that server terminals and controlled terminals are different in their functions and prices.
Basically, for terminals such as home electric appliances that are added from time to time and various usages can also be assumed, the relationship between terminals should be equal. However, there is no conventional method known for creating a group when all the terminals are in equal relationships.
Now, in consideration of the foregoing problems, the device authentication system according to the present invention enables terminals to determine other terminals that belong to a same group, when terminals are in equal relationships with each other.
Also, in the device authentication system according to the present invention, an object is for a terminal to be able to obtain a list of devices that belong to a same group in a secure manner, before the terminal carries out processing such as authentication or content transmission that gives a heavy load to the terminal. Furthermore, in the device authentication system according to the present invention, another object is that by using the aforementioned group list, a terminal is able to determine to which device it will send transmitting data, and realizes efficient utilization of a communication channel by not communicating with terminals that are not allowed to obtain certain content.
Another object of the present invention is to provide a device authentication system that is capable of contributing to the future popularization of network distribution of charged content.